1. Field of the Invention
The present invention relates to building construction materials and techniques and, in particular, to an assembly to interconnect building members and anchor structures.
2. Description of the Related Art
In typical residential and light industrial/commercial building frame wall construction, load bearing frame walls are comprised of a series of studs and posts that are anchored to the foundation and covered with sheathing material installed over both sides of the frame. Typically, the frame is constructed from a number of vertically extending studs that are positioned between and interconnected with upper and lower plates. The lower plates and/or vertical studs are typically anchored to the foundation in some fashion. The covering material, plywood, sheet rock, siding, plaster, etc. is then attached over the studs.
Natural forces commonly occur that impose vertical and horizontal forces on the structural elements of the buildings. These forces can occur during earth movement in an earthquake and from high wind conditions such as occur during hurricanes, tornadoes, cyclones, or other extreme weather conditions. If these forces exceed the structural capacity of the building, they can cause failures leading to damage to or the collapse of the building with resultant economic loss and potential injuries and loss of life.
In order to mitigate these natural forces, prudent architectural engineering design and practice and many building codes require the use of what is known as lateral shear reinforcement. Shear reinforcement is a two-fold process. A first facet involves strengthening the structure of a wall to increase the capacity of a wall to resist horizontal deflection of the top member relative the bottom member in the plane of the wall. The second facet of shear reinforcement involves positively attaching the wall structure to the underlying foundation to inhibit uplift and overturning of the wall assembly from the foundation. If a building lifts off the foundation, it suffers further damage when gravity draws it back into contact with the ground. Effective shear reinforcement must be resistant to repeated, cyclic forces over a period of time.
With wood frame construction, wall strengthening has been traditionally accomplished with a method known as sheathing the frame structure with a diaphragm. Typically, this involves attaching a solid sheet of material, such as plywood, oriented strand board, gypsum board, cement plaster, sheet steel, etc. to the wall studs with nails or screws. The sheathing is nailed or screwed around the periphery of the diaphragm to the underlying wood studs with a spacing and placement determined by engineering analysis. Diaphragms employ commonly available materials and tools and utilize known construction techniques.
An alternative method of strengthening walls in common practice incorporates what are known as shear panels that can offer strength and labor and material advantages over sheathing an entire structure. Concentrated shear panel members are panels or other reinforcing shapes that are highly resistant to deformation and that are interconnected with the vertical frame studs or posts of the building frame. Shear panel members can be supplied as pre-assembled units that are installed at the construction site or can be assembled in place at the job site.
A typical method of securing a frame to a foundation is to connect one end of a length of metal strapping to an end of wall stud and to embed the other end in the concrete foundation. Uplift forces acting on the building frame are resisted through the embedded strap. The use of metal strapping is convenient to install, but has strength limitations to inhibit uplift.
An alternative method of anchoring the building involves attaching metal brackets, commonly referred to as hold-downs, directly to frame studs or end posts of the shear member which are in turn attached to anchors comprised of bolts or threaded rods embedded in a concrete foundation. While having greater capacity than metal strapping, the bracket hold-down method of anchoring a building frame has some potential installation complications. If the anchor extends too far above the foundation surface, many existing hold-down designs can not be used or at least require that the worker carefully remove some of the anchor length in a manner that does not damage the threads thereby preventing the proper attachment of the securing fastener. If the anchor does not extend far enough from the foundation surface, no provision is made to allow for the deficit and the assembly is unusable resulting in time delays and costly rework.
A second installation complication concerns the placement of the hold-downs. Hold-downs are typically used in pairs and are placed at each frame stud or end post that encloses the diaphragm or shear panel member. Corresponding anchors are set in pairs into the foundation. Prudent construction practice involves the utilization of setting templates which hold the anchors in place while concrete is poured around them. The anchors are held in place with the templates that hold them upright and fix their location until the concrete is poured and sets. The templates accurately set the relative spacing of the anchor pairs. However there is a degree of difficulty in accurately placing all of the multiple templates that are used for a typical building frame with respect to each other and there is typically some misplacement of the anchor pairs. It can be appreciated that once an anchor is set in a foundation it is effectively permanently fixed in place.
Many existing hold-down products fit precisely over the protruding anchors with minimal clearance. Thus they fix the location of the attached studs or end posts as well. It can be seen that misplacement of the templates and anchors will cause misalignment of the wall frame sections or shear panel member end posts with resultant difficulties and delays in construction. A larger through hole can be provided in many holdowns to provide additional clearance, however this requires additional components such as washer plates to compensate for the oversized bolt hole.
Another need in existing construction materials and techniques arises with respect to the vertical loads carried by a building""s frame. The gravity weight of a building and its contents direct a vertical load that is typically transferred to and carried by the vertical load bearing studs of the building""s frame. These vertical studs typically bear at their lower end on a pressure treated mudsill.
A mudsill typically comprises a number of 2xc3x974 pieces of lumber placed directly on a foundation so as to lay on the face defined by the 4xe2x80x3 dimension and the longest dimension. A mudsill is also used as a nailing surface along the lower extent of the exterior walls. The inherent structural problem with the mudsill, comprising a wooden member, is that it has less capacity to resist crushing because of the orientation of the grain of the wood. A compressive distortion in the mudsill allows the vertical load-bearing studs to move downwards due to the incident vertical load. Compressive movement of the vertical end studs in a shear panel creates deflection in the walls of the building, weakening the overall structure, providing impetus for cracks to form in the external and interior wall finishings, and potentially concentrating load stresses in unforeseen and damaging ways. In particular, movement of frame members enclosing a shear member will pre-load the shear member and, depending on the magnitude of movement, possibly distort the shear member. Pre-loading and distortion of shear members can seriously compromise their structural strength.
Shear reinforcement becomes more complicated with multiple story buildings. A multi-story building requires shear reinforcement of even higher capacity that a single story building. The taller walls of a multi-story present a greater area for wind forces to bear on and a longer moment arm for wind and seismic forces. The ultimate capacity requirements of a shear panel reinforcement system increases rapidly as the building grow taller. Because of this, shear reinforcement is required to be incorporated into all levels of a building, including the upper level walls. The particular difficulty with shear reinforcing upper stories of a building is that shear assemblies placed within upper story walls are no longer adjacent the building""s foundation as the ground level walls are. Forces from incident wind or seismic activity ultimately must be transferred to the load bearing foundation. It should also be appreciated that the previously mentioned concerns with vertical loading and damage to supporting mudsills are exacerbated with multi-story structures. Wood shrinkage over time in upper story framing contributes to problems with excessive deflection in shear panel assemblies.
From the foregoing, it can be appreciated that there is a continuing need for a method and device to continuously secure and anchor a building frame to a foundation. Moreover there is a particular need for a manner of securing shear panel assemblies to foundations in a manner that allows for both lateral or vertical misplacement of the anchoring elements in the foundation with respect to the hold-down assembly without a loss of structural integrity and capacity of the shear assembly as a whole or requiring rework. The desired anchoring method should be convenient to install, yet offer strength advantages to the existing use of metal strapping. It would be an additional advantage for the device to be capable of supporting vertical compression loads as well as tension loads to thereby enable the device to transfer loads directly to the foundation to compensate for wood shrinkage and to bypass the mudsill as a compression resisting element in the shear panel system and to allow the device to interconnect upper story shear assemblies in multi-story buildings.
The aforementioned needs are satisfied by the anchor interconnect device of the present invention which in one aspect is an assembly for interconnecting building members so as to resist tension and compression forces. The assembly is adapted to transfer both tension and compression forces along an axis such that the assembly can transfer uplift forces that impart on a building due to wind force or earth movement to an underlying foundation. Transferring the forces to a relatively massive foundation resting on and partially within the ground increases the ability of the building employing the anchor interconnect devices to resist uplift forces without suffering damage.
By transferring compression forces to the foundation through the vertical grain elements of a wood frame wall, the anchor interconnect device of the present invention directs the vertical loads arising from the weight of the building and its contents directly to the foundation. Thus, the anchor interconnect device of the present invention substantially by-passes a mudsill placed on the foundation and at the lower extent of the walls as a compressive load bearing member. The anchor interconnect device permits the weight of the building and its contents to minimally bear on the mudsill and thus minimizes the deleterious effects of wall deflection caused by the building""s weight bearing on the mudsill.
In another aspect of the invention, the anchor interconnect device provides a limited freedom of motion between the anchor interconnect device and an attached building member along a second axis perpendicular to a wall of a building. By allowing a limited freedom of motion, the anchor interconnect device accommodates some misplacement of anchor structures in a foundation without requiring rework, but still substantially maintains the intended placement of walls and the full strength capacity of the anchor interconnect device.
In yet another aspect of the invention, the anchor interconnect device provides a range of motion along a first axis for interconnecting building members. By providing a range of motion, the anchor interconnect device accommodates variation in relative proximity of the building members, while still being able to interconnect them without significantly compromising the strength of the anchor interconnect device or the overall structure.
In yet another aspect, the anchor interconnect device is an assembly for interconnecting building members so as to resist tension forces. The anchor interconnect device in this aspect is intended for use in building applications that only require transfer of tension loads. The anchor interconnect device of this embodiment comprises fewer component pieces and installation steps than the device of the embodiment which transfers tension and compression loads and is thus even less expensive to produce, purchase, and install. The anchor interconnect devices of these two embodiments offer the construction trades the option of a more capacious device where needed and a somewhat simplified, lower cost device for applications which do not require the additional compression resisting capability.
The anchor interconnect device includes an attachment member with provision to allow the member to be securely attached to a structure. The attachment member is a rigid structure and reinforces the structure member against flexing and distortion due to tension and compression forces. The attachment member also provides increased area for transferring forces from the structure through the anchor interconnect device to an anchor structure, which increases the capacity of the device, in particular its resistance, to cyclic forces. In one embodiment, the anchor interconnect device also includes load transfer plates to provide additional bearing surface for the anticipated uplift and weight forces and to transfer forces through the assembly. The load transfer plates further inhibit distortion and damage to the anchor interconnect device and to the attached structure members.
It can be appreciated that the anchor interconnect device, comprising few component pieces interconnected with few common fasteners or joining methods can be readily assembled in the field. By allowing a restricted freedom of motion perpendicular to the plane of a wall, it can be seen that the anchor interconnect device can accommodate a degree of misplacement of the embedded anchor element. This will allow construction workers to more easily align the wall members together and thus improve the speed and economy of construction. By allowing the attachment of the anchor interconnect device either directly to an anchor member or with an anchor attachment member and a coupler, the anchor interconnect device provides for variation in the protrusion of the anchor member from the foundation surface. These and other objects and advantages will become more fully apparent from the following description taken in conjunction with the accompanying drawings.